/**
 *    Copyright 2009-2017 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.parsing;

/**普通记号解析器，处理#{}和${}参数
 *
 * @author Clinton Begin
 */
public class GenericTokenParser {

	// 有一个开始和结束记号
	private final String openToken;
	private final String closeToken;
	// 记号处理器
	private final TokenHandler handler;

	public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {
		this.openToken = openToken;
		this.closeToken = closeToken;
		this.handler = handler;
	}

	public String parse(String text) {
		if (text == null || text.isEmpty()) {
			return "";
		}
		// 获取第一个#{在SQL中的位置
		int start = text.indexOf(openToken, 0);
		if (start == -1) {
			// start为-1说明SQL中不存在任何#{}参数占位符
			return text;
		}
		// 将sql转换为char数组
		char[] src = text.toCharArray();
		// offset用于记录已解析#{或者}的偏移量，避免重复解析
		int offset = 0;
		final StringBuilder builder = new StringBuilder();
		// expression为#{}中的参数内容
		StringBuilder expression = null;
		// 遍历获取所有#{}参数占位符的内容，例如：#{favouriteSection,jdbcType=VARCHAR}，然后调用TokenHandler的handleToken方法替换参数占位符
		// 这里是循环解析参数，参考GenericTokenParserTest，比如可以解析${first_name} ${initial}
		// ${last_name} reporting.这样的字符串，里面有3个 ${}
		while (start > -1) {
			// 判断一下 ${ 前面是否是反斜杠，这个逻辑在老版的mybatis中（如3.1.0）是没有的
			if (start > 0 && src[start - 1] == '\\') {
				// this open token is escaped. remove the backslash and continue.
				// 新版已经没有调用substring了，改为调用如下的offset方式，提高了效率
				builder.append(src, offset, start - offset - 1).append(openToken);
				offset = start + openToken.length();
			} else {
				// found open token. let's search close token.
				if (expression == null) {
					expression = new StringBuilder();
				} else {
					expression.setLength(0);
				}
				builder.append(src, offset, start - offset);
				offset = start + openToken.length();
				int end = text.indexOf(closeToken, offset);
				while (end > -1) {
					if (end > offset && src[end - 1] == '\\') {
						// this close token is escaped. remove the backslash and continue.
						expression.append(src, offset, end - offset - 1).append(closeToken);
						offset = end + closeToken.length();
						end = text.indexOf(closeToken, offset);
					} else {
						expression.append(src, offset, end - offset);
						offset = end + closeToken.length();
						break;
					}
				}
				if (end == -1) {
					// close token was not found.
					builder.append(src, start, src.length - start);
					offset = src.length;
				} else {
					// 得到一对大括号里的字符串后，调用handler.handleToken，比如替换变量这种功能
					builder.append(handler.handleToken(expression.toString()));
					offset = end + closeToken.length();
				}
			}
			start = text.indexOf(openToken, offset);
		}
		if (offset < src.length) {
			builder.append(src, offset, src.length - offset);
		}
		return builder.toString();
	}
}
